1. Field of the Invention
The present invention relates to means and method for producing orthogonal and angular motions, singly and in combination. In a preferred embodiment, these motions are utilized for precise and micron adjustment between relatively moveable elements.
2. Description of the Prior Art
There is a recongized need for smaller electronic devices such as for acoustic wave, integrated optic, superconducting weaklink, and semiconductor purposes, including discrete transistor, LSI, MSI, and SSI semiconductor devices. The smallest of possible devices that can be presently mass manufactured outside of laboratory fabrication are limited by their size to approximately 5 micron line width due to conventional photolithographic limitations resulting from scattering, reflection and diffraction of light, such as ultraviolet light. In the laboratory, 1 micron lines can be produced utilizing ultraviolet light; however, the precision available and used in laboratories is not economically available for mass production.
It is known that smaller than 1 micron size lines can be obtained using x-ray lithography, for example, see D. L. Spears and H. I. Smith, "High Resolution Pattern Replication Using Soft X-rays," Electronics Letters 8, 102 (1972); D. L. Spears and H. I. Smith, "X-ray Lithography -- A New High Resolution Replication Process," Solid State Technology, July 1972, pages 21-26; D. L. Spears, H. I. Smith and E. Stern, "X-ray Replication of Scanning Electron Microscope Generated Patterns," Proceedings of the Fifth International Conference on Electron and Ion Beam Science and Technology (May 1972, Houston) Electrochemical Society, Princeton, 1972, page 80; and H. I. Smith and D. L. Spears, "X-ray Lithography: Complimentary Technique to Electron Beam Lithography," Journal of Vacuum Science and Technology, 10, 913 (1973).
There are several reasons for obtaining smaller devices. In LSI and related work, it is desired to place as much circuitry and components in the smallest possible area, thereby increasing density for cost, weight and space considerations. Certain electronic devices, such as microwave, acoustic wave, and other semiconductor devices, operate more efficiently with maximum performance, and at higher frequencies when they are smaller. Integrated optical circuitry can operate more efficiently when fabricated with perfections which are smaller than the wavelength of light.
In the prior art, replication of patterns has been accomplished by photolithography using ultraviolet light, subject to the resolution limitations described above. Other prior art accomplished replication by parallel electron projection of images from a patterned photocathode, which can provide better resolution than photolithography, for example, see T. W. O'Keefe, "Fabrication of Integrated Circuits Using the Electron Image Projection System," IEEE Transactions ED-17, 465 (1970); W. R. Livesay, "Electron Image Projection Systems for Microcircuit Lithography," IEEE Transactions ED-19, 647 (1972); and W. R. Livesay, "Integrated Circuit Production with Electron Beams," Journal of Vacuum Science and Technology, 10, 1028 (1973).
In the case of photolithographic replication using ultraviolet light, the mask pattern need only be registered to a wafer with an accuracy of about 1 micron. This is accomplished in the prior art by mechanical linkages such as a pantograph. These mechanical linkages are not sufficiently accurate for the submicron registration accuracies required for the high resolution pattern replication accomplished by parallel electron projection or x-ray lithography. These mechanical mask alignment systems have been used under a feedback electrical control for automatic alignment of the wafer to the mask pattern, for example, see K. G. Clark, "Automatic Mask Alignment in MOS/LGI Processing, " Solid State Technology, February 1971, pages 48-54. A serious drawback to these systems is the low constrast of the registration marks on the processed wafer available to the image detection system when using ultraviolet light.
In the case of parallel electron projection, the image of the mask pattern may be registered to a wafer by manipulating this image with a magnetic field transferse to the electron beam; however, this system has several drawbacks. Electron deflection creates distortions and aberrations in the image; image rotation is accompanied by skew. Furthermore, the beam must be extraordinarily shielded against undesired external magnetic disturbances. Thus it is generally preferable to utilize some mechanical movement for moving the wafer and/or the mask with respect to a beam rather than to control the beam movement. When the beam consists of soft x-rays, the option of moving the beam does not exist, because the soft x-ray beam cannot be influenced by external fields.
Micromovement control systems are known, see J. B. Pawley, "A Dual Needle Piezoelectric Micromanipulator for the Scanning Electron Microscope", The Review of Scientific Instruments, 43, 600 (1972), F. L. N-Nagy and G. C. Joyce, "Micromovement Control Systems", International Federation of Automatic Control, Fifth World Congress, Paris, France, June 12-17, 1972, Proceedings, Part 2 (A73-24001 10-10) Dusseldorf, International Federation of Automatic Control, 1972, Pages 23.6.1-23.6.9. However, none of these systems are designed to obtain the combination of orthogonal (X-Y) and angular (0) micromovements under an electrical control, as required for a lithographic registration system.
Furthermore, prior art systems are deficient in that they use bearings which leads to friction and contacting surfaces, resulting in relative lack of control for movements of less than one micron. Friction precludes perfectly smooth movement between surfaces while micron imperfections of contacting surfaces additionally cause slight movement of the surfaces towards and away from each other.
A micromovement control system has been used with a parallel electron projection lithographic system, see J. E. Piquendar, "Nanoelectronics," Proceedings of the Fifth International Conference on Electron and Ion Beam Science and Technology, May 1972, Houston, Electrochemical Society, Princeton, 1972, Page 31 and J. E. Piquendar, "Nanoelectronic Project and ASTEC Logic," Journal of Vacuum Science and Technology, 10, 1132 (1973). The precise system described by Piquendar is not known; however, it is believed that this system does not produce orthogonal and angular micromovements both singly and in combination and also does not eleiminate contacting surfaces.